Master control device and synchronous communication system using same

Abstract

A master control device connected to a plurality of slave control devices via a network is configured to include an own local time counted by a counter unit, in a message and transmit the message to the slave control devices by the timing synchronization unit, calculate a difference between a reception time of a message transmitted from the slave control device, which has received the message, at a timing corrected in accordance with the local time and a pre-calculated message reception predicted time by a timing synchronization determination unit, calculate a correction amount for timing of the slave control devices using the difference by a timing synchronization correction unit, add the correction amount to the local time, include the local time in a message, and transmit the message to the slave control devices.

What is claimed is: 
     
       1. A master control device connected to a plurality of slave control devices via a network, the master control device comprising at least one processor comprising:
 a master-side timing synchronizer for including an own local time in a first message and transmitting the first message to the slave control devices; 
 a message reception difference calculator for calculating a difference between a reception time of a second message transmitted from the slave control device at a timing corrected in accordance with the local time and a pre-calculated message reception predicted time; and 
 a timing correction amount calculator for calculating a correction amount for timing of the slave control devices by using the difference calculated by the message reception difference calculator, 
 wherein the pre-calculated message reception predicted time is set to a sum of the local time, a message delay time of the slave control device, and an activation waiting time that is a time taken until a message transmission task of the slave control device is activated to send the second message since receipt of the first message. 
 
     
     
       2. The master control device according to  claim 1 , wherein the correction amount calculated by the timing correction amount calculator is added to the local time and included in the first message, and the first message is transmitted by the master-side timing synchronizer to the slave control devices. 
     
     
       3. A master control device connected to a plurality of slave control devices via a network, the master control device comprising at least one processor comprising:
 a master-side timing synchronizer for including an own local time in a first message and transmitting the first message to the slave control devices; 
 a message reception difference calculator for calculating a difference between a reception time of a second message transmitted from the slave control device at a timing corrected in accordance with the local time and a pre-calculated message reception predicted time; 
 a timing correction amount calculator for calculating a correction amount for timing of the slave control devices by using the difference calculated by the message reception difference calculator; and 
 a database in which information to be used for the calculation by the message reception difference calculator is stored, wherein 
 information of a schedule table for managing activation timing of a task of the slave control device transmitting the second message, and the pre-calculated message reception predicted time are stored in the database. 
 
     
     
       4. The master control device according to  claim 2 , further comprising a database in which information to be used for the calculation by the message reception difference calculator is stored, wherein
 information of a schedule table for managing activation timing of a task of the slave control device transmitting the second message, and the pre-calculated message reception predicted time are stored in the database. 
 
     
     
       5. The master control device according to  claim 3 , further comprising a message reception time predictor for calculating the message reception predicted time by using the activation timing of the task on the schedule table stored in the database. 
     
     
       6. The master control device according to  claim 4 , further comprising a message reception time predictor for calculating the message reception predicted time by using the activation timing of the task on the schedule table stored in the database. 
     
     
       7. A master control device connected to a plurality of slave control devices via a network, the master control device comprising at least one processor comprising:
 a master-side timing synchronizer for including an own local time in a first message and transmitting the first message to the slave control devices; 
 a message reception difference calculator for calculating a difference between a reception time of a second message transmitted from the slave control device at a timing corrected in accordance with the local time and a pre-calculated message reception predicted time; and 
 a timing correction amount calculator for calculating a correction amount for timing of the slave control devices by using the difference calculated by the message reception difference calculator, wherein 
 the message reception difference calculator calculates the difference for each of the slave control devices, and 
 the timing correction amount calculator includes:
 setting one of the differences of the plurality of slave control devices calculated by the message reception difference calculator, as a provisional correction amount; 
 comparing the difference of each slave control device with the provisional correction amount, and count the number of slave control devices for each of which a difference between the difference and the provisional correction amount is within a threshold, for each provisional correction amount; and 
 
 determining a provisional correction amount for which the number of counts is the largest, as the correction amount. 
 
     
     
       8. The master control device according to  claim 2 , wherein
 the message reception difference calculator calculates the difference for each of the slave control devices, and 
 the timing correction amount calculator includes:
 setting one of the differences of the plurality of slave control devices calculated by the message reception difference calculator, as a provisional correction amount; 
 comparing the difference of each slave control device with the provisional correction amount, and count the number of slave control devices for each of which a difference between the difference and the provisional correction amount is within a threshold, for each provisional correction amount; and 
 
 determining a provisional correction amount for which the number of counts is the largest, as the correction amount. 
 
     
     
       9. The master control device according to  claim 3 , wherein
 the message reception difference calculator calculates the difference for each of the slave control devices, and 
 the timing correction amount calculator includes:
 setting one of the differences of the plurality of slave control devices calculated by the message reception difference calculator, as a provisional correction amount; 
 comparing the difference of each slave control device with the provisional correction amount, and count the number of slave control devices for each of which a difference between the difference and the provisional correction amount is within a threshold, for each provisional correction amount; and 
 determining a provisional correction amount for which the number of counts is the largest, as the correction amount. 
 
 
     
     
       10. The master control device according to  claim 4 , wherein
 the message reception difference calculator calculates the difference for each of the slave control devices, and 
 the timing correction amount calculator includes:
 setting one of the differences of the plurality of slave control devices calculated by the message reception difference calculator, as a provisional correction amount; 
 comparing the difference of each slave control device with the provisional correction amount, and count the number of slave control devices for each of which a difference between the difference and the provisional correction amount is within a threshold, for each provisional correction amount; and 
 
 determining a provisional correction amount for which the number of counts is the largest, as the correction amount. 
 
     
     
       11. The master control device according to  claim 5 , wherein
 the message reception difference calculator calculates the difference for each of the slave control devices, and 
 the timing correction amount calculator includes:
 setting one of the differences of the plurality of slave control devices calculated by the message reception difference calculator, as a provisional correction amount; 
 comparing the difference of each slave control device with the provisional correction amount, and count the number of slave control devices for each of which a difference between the difference and the provisional correction amount is within a threshold, for each provisional correction amount; and 
 
 determining a provisional correction amount for which the number of counts is the largest, as the correction amount. 
 
     
     
       12. The master control device according to  claim 6 , wherein
 the message reception difference calculator calculates the difference for each of the slave control devices, and 
 the timing correction amount calculator includes:
 setting one of the differences of the plurality of slave control devices calculated by the message reception difference calculator, as a provisional correction amount; 
 comparing the difference of each slave control device with the provisional correction amount, and count the number of slave control devices for each of which a difference between the difference and the provisional correction amount is within a threshold, for each provisional correction amount; and 
 
 determining a provisional correction amount for which the number of counts is the largest, as the correction amount. 
 
     
     
       13. A synchronous communication system comprising:
 the master control device according to  claim 1 ; and 
 a plurality of slave control devices connected to the master control device via a network and performing timing synchronization with the master control device. 
 
     
     
       14. A synchronous communication system comprising:
 the master control device according to  claim 2 ; and 
 a plurality of slave control devices connected to the master control device via a network and performing timing synchronization with the master control device. 
 
     
     
       15. A synchronous communication system comprising:
 the master control device according to  claim 3 ; and 
 a plurality of slave control devices connected to the master control device via a network and performing timing synchronization with the master control device. 
 
     
     
       16. A synchronous communication system comprising:
 the master control device according to  claim 4 ; and 
 a plurality of slave control devices connected to the master control device via a network and performing timing synchronization with the master control device. 
 
     
     
       17. A synchronous communication system comprising:
 the master control device according to  claim 5 ; and 
 a plurality of slave control devices connected to the master control device via a network and performing timing synchronization with the master control device. 
 
     
     
       18. A synchronous communication system comprising:
 the master control device according to  claim 6 ; and 
 a plurality of slave control devices connected to the master control device via a network and performing timing synchronization with the master control device. 
 
     
     
       19. A synchronous communication system comprising:
 the master control device according to  claim 7 ; and 
 a plurality of slave control devices connected to the master control device via a network and performing timing synchronization with the master control device. 
 
     
     
       20. The synchronous communication system according to  claim 13 , wherein each of the slave control devices includes:
 a schedule table for managing activation timing of a task of transmitting the second message; and 
 a slave-side timing synchronizer for correcting the activation timing of the task on the schedule table in accordance with the local time included in the first message transmitted from the master control device, and transmitting the second message to the master control device.